1. Field of the Invention
This invention relates to a lofty, nonwoven material produced from continuous fibers in which the lofty character of the nonwoven material is the result of the fibers comprising the web being oriented in a z-direction, that is outside of the plane of the orientation of the web, of the nonwoven material. These materials are particularly suitable for use in a broad range of applications including fluid management (surge), air and liquid filtration, acoustic and thermal insulation, packing material, absorbents, and cleaning materials. More particularly, these materials are suitable for use as surge, spacer layers, filtration materials and absorbent layers in personal care absorbent products including disposable diapers, incontinence garments, and feminine care products such as sanitary pads and napkins, and in face masks, surgical gowns, sterile wraps and surgical drapes. In addition, this invention relates to methods for producing such lofty, nonwoven materials.
2. Discussion of Related Art
Absorbent personal care articles such as sanitary pads and napkins, disposable diapers, incontinent-care pads and the like are widely used, and much effort has been made to improve their effectiveness and functionality. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. The purpose of this cover material is to help structurally contain the absorbent material and to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically of relatively low basis weight nonwoven fabric. Improved product performance has been obtained in these products through the incorporation of a surge management material disposed between the cover material and the absorbent material. The surge management material is made from a relatively high basis weight, low density, that is, thick, nonwoven web material.
In nonwoven webs, the fibers comprising the web are generally oriented in the x-y plane of the web and the resulting nonwoven web material is relatively thin, that is lacking in loft or significant thickness. Loft or thickness in a nonwoven web suitable for use in personal care absorbent articles promotes comfort (softness) to the user, surge management and fluid distribution to adjacent layers.
In order to impart loft or thickness to a nonwoven web, it is generally desirable that at least a portion of the fibers comprising the web be oriented in the z-direction. Conventionally, such lofty nonwoven webs are produced using staple fibers. See, for example, U.S. Pat. No. 4,837,067 which teaches a nonwoven thermal insulating batt comprising structural staple fibers and bonding staple fibers which are entangled and substantially parallel to the faces of the batt at the face portions and substantially perpendicular to the faces of the batt, and U.S. Pat. No. 4,590,114 which teaches a batt including a major percent of thermo-mechanical wood pulp fibers stabilized by the inclusion of a minor percent of thermoplastic fibers including staple length thermoplastic fibers. Alternatively, conventional high loft forming processes rely on pre-forming processes such as fiber crimp formed on a flat wire or drum, and post-forming processes such as creping or pleating of the formed web.
In contradistinction to the known art, the present invention does not first form a web of material and pleat it. Rather, fibers are looped, or bent, on themselves without being first being formed into a material web. These fiber level loops, running between the major surfaces of the resultant web, are aggregated in the cross machine direction to form structures running in the cross machine direction which are herein sometimes called xe2x80x9cwavesxe2x80x9d or xe2x80x9cfoldsxe2x80x9d to distinguish them from xe2x80x9cpleatsxe2x80x9d which refer to structures in preformed web or mesh material that has been folded on itself.
Accordingly, it is one object of this invention to provide a high loft, low density nonwoven web material comprising substantially continuous fibers as opposed to staple fibers traditionally used in the manufacture of such nonwoven materials.
This and other objects of this invention are addressed by a lofty, nonwoven material comprising a nonwoven web comprising a plurality of substantially continuous fibers, which may be crimped or linear, oriented in a z-direction of the nonwoven web. The substantially continuous fibers are preferably spunbond and/or meltblown. In accordance with one embodiment of this invention, a support structure may be attached to at least one face of the nonwoven web, thereby providing strength to the high loft nonwoven web. This laminate structure provides support for the high loft structure, strength for winding, converting, etc., and a boundary layer to either enhance or retard fluid flow into the lofty absorbent structure in products such as disposable diapers, incontinence garments, and absorbent feminine care products including sanitary pads and napkins.
The lofty, nonwoven material of this invention is produced in accordance with one embodiment of this invention by a process in which a plurality of substantially continuous fibers are directed into a variable nip, resulting in bending of the fibers and formation of a nonwoven web. Within the nip the fibers may be subjected to a vacuum from both sides of the nip, either equally or differentially, producing a lofty, nonwoven web having a plurality of the substantially continuous fibers oriented in a z-direction.
In accordance with another embodiment of this invention, the lofty, nonwoven material is produced by directing a plurality of continuous, substantially linear, filament fibers through a slot formed by two opposed surfaces whereby the substantially continuous fibers bend from contact with the two opposed surfaces, which may be differential speeds or vacuum, or both, thereby forming a lofty, nonwoven web having a plurality of as-formed z-direction fibers.